Figure 17a. Plexiform neurofibromas of the bladder and prostate in a 21-year-old man with NF1 who was being evaluated for infertility. (a) Sagittal T1-weighted MR image shows a large hypointense mass (*) infiltrating the posterior bladder wall. The mass extends inferiorly to involve the prostate (arrow) and perineum. (b) Axial T2-weighted MR image shows a ringlike (arrow) and septated pattern, consistent with the fascicular pattern of plexiform neurofibromas.